Valve actuation system having grooved adjusting screw

ABSTRACT

A valve actuation system is disclosed for an internal combustion engine. The system may have a gas exchange valve, a rocker arm pivotally connected to a shaft, a pushrod, a lash adjuster disposed in the pushrod. The system may also have an adjusting screw disposed in the rocker arm and configured to engage and fluidly supply the lash adjuster. The adjusting screw may include a shaft having a threaded outer annular surface, and a head connected to the shaft and having a rounded outer surface and a flat end face. The adjusting screw may also include an axial passage passing through the flat end face, a radial passage formed in the shaft and extending from the threaded bore of the rocker arm to the axial passage, and at least one radial groove formed in the rounded outer surface of the head and passing through the axial passage.

TECHNICAL FIELD

The present disclosure is directed to a valve actuation system and, more particularly, to a valve actuation system having an adjusting screw with oil distribution grooves.

BACKGROUND

Each cylinder of an internal combustion engine is equipped with one or more gas exchange valves (e.g., intake and exhaust valves) that are cyclically opened during normal operation to allow fuel and air into the engine and to discharge exhaust from the engine. In a conventional engine, the valves are opened by way of a camshaft/rocker arm arrangement. The camshaft includes one or more lobes oriented at particular angles corresponding to desired lift timings and amounts of the associated valves. The cam lobes are connected to stem ends of the associated valves by way of the rocker arm and associated pushrod linkage. As the camshaft rotates, the cam lobes come into contact with a first pivoting end of the rocker arm, thereby forcing a second pivoting end of the rocker arm against the stem ends of the valves. This pivoting motion causes the valves to lift or open against a spring bias. As the cam lobes rotate away from the rocker arm, the valves are released and allowed to return to their closed positions.

Over time, components of the engine (e.g., the valves, associated seats, rocker arm, pushrod linkage, etc.) wear, creating clearances or spaces between the components. These clearances can cause the valves to not open or close properly. When this happens, the engine can become noisy, lose performance, and wear at an accelerated rate. Accordingly, the clearances should be periodically checked and adjusted.

One way to adjust these clearances is through the use of an adjusting screw. A typical adjusting screw is located at a cam-end of the rocker arm, and has a spherical head that extends from the rocker arm into a rounded socket of an associated pushrod. The adjusting screw is selectively turned to extend a greater distance from the rocker arm toward the pushrod as the engine wears, thereby taking up any clearance that has developed due to the wear.

An exemplary adjusting screw is disclosed in WO Patent No. 2012153102 of Wotherspoon that published on Nov. 15, 2012 (“the '102 patent”). In particular, the '102 patent discloses a connection member having a shank inserted into a bore of a rocker arm. The shank is cylindrical and provided with an outer thread that engages an inner thread of the bore. An outer head is provided at a top end of the shank to allow the connection member to be adjusted relative to the rocker arm, thereby eliminating slack in an associated valve train. The connection member also includes a spherical pivot head at an opposite end that is configured to be inserted into a spherical socket of an associated pushrod, thereby permitting relative articulation of the connection member. A lubricant channel is formed in the connection member, and extends from an exit hole in the spherical pivot head to an annular recess located just below the outer head. One or more radial grooves are machined into the spherical pivot head to promote the dispersion of lubricant from the lubricant channel within an area between the spherical outer surface of the pivot head and the socket of the pushrod. The grooves extend from an annular periphery of a contact area centered at the pivot head towards a peripheral edge. A width and depth of the grooves increases away from the exit hole. Due to little clearance between the pivot head and the socket inside the contact area, the pressure of the lubricant flowing therethrough creates a film bearing for loads transmitted between the connecting member and the pushrod.

Although the connection member of the '102 patent may function well as an adjusting screw in many applications, it may be less than optimal in other applications. For example, in some applications, it may require too much pressure to adequately separate the connecting member from the pushrod socket and create the film bearing, and the high-pressure flow through the constricted contact area may not properly cool the interface. In addition, the variable width and depth of the grooves, along with the method of fabricating the grooves, may increase a cost of the connection member.

The valve actuation system of the present disclosure is directed towards overcoming one or more of the problems set forth above and/or other problems of the prior art.

SUMMARY

One aspect of the present disclosure is directed to an adjusting screw for a valve actuation system. The adjusting screw may include an elongated cylindrical shaft having a first end, a second end, and a threaded outer annular surface extending between the first and second ends. The adjusting screw may also include a head connected to the elongated cylindrical shaft at the first end and having a rounded outer surface, an axial passage formed in the elongated cylindrical shaft and passing through the head, and at least one radial groove formed in the rounded outer surface of the head and connected with the axial passage.

Another aspect of the present disclosure is directed to another adjusting screw for a valve actuation system. This adjusting screw may include an elongated cylindrical shaft having a first end, a second end, and a threaded outer annular surface extending between the first and second ends. The adjusting screw may also include a head connected to the elongated cylindrical shaft at the first end and having a rounded outer surface, and an axial passage formed in the elongated cylindrical shaft and passing through the head. The adjusting screw may further include a flat end face formed at a center of the rounded outer surface around the axial passage, and at least one radial groove formed in the rounded outer surface of the head.

Yet another aspect of the present disclosure is directed to a valve actuation system. The valve actuation system may include at least one gas exchange valve, a shaft, and a rocker arm pivotally connected to the shaft. The rocker arm may have a first end operatively engaged with the at least one gas exchange valve, a second end with a threaded bore, and a passage extending from the shaft to the threaded bore. The valve actuation system may also include a pushrod with a cam end and a rocker arm end, a lash adjuster disposed in the rocker arm end of the pushrod, and an adjusting screw disposed in the second end of the rocker arm and configured to engage and fluidly supply the lash adjuster in the pushrod. The adjusting screw may have an elongated cylindrical shaft with a first end, a second end, and a threaded outer annular surface extending between the first and second ends, and a head connected to the elongated cylindrical shaft at the first end and having a rounded outer surface and a flat end face formed at a center of the rounded outer surface. The adjusting screw may also have an axial passage formed in the elongated cylindrical shaft and passing through the flat end face of the head, a radial passage formed in the elongated cylindrical shaft and extending from the threaded bore of the rocker arm to the axial passage, and at least one radial groove formed in the rounded outer surface of the head and passing through the axial passage.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic illustration of an exemplary disclosed engine;

FIG. 2 is a cross-sectional illustration of an exemplary disclosed valve actuation system that may be used with the engine of FIG. 1; and

FIGS. 3 and 4 are isometric and cross-sectional illustrations, respectively, of an exemplary disclosed adjusting screw that may be included in the valve actuation system of FIG. 2.

DETAILED DESCRIPTION

FIG. 1 illustrates an engine 10 equipped with an exemplary disclosed valve actuation system 12. For the purposes of this disclosure, engine 10 is depicted and described as a four-stroke diesel engine. One skilled in the art will recognize, however, that engine 10 may embody any type of combustion engine such as, for example, a two- or four-stroke, gasoline or gaseous fuel-powered engine. As will be described in more detail below, valve actuation system 12 may help regulate fluid flows through engine 10.

Engine 10 may include an engine block 14 that at least partially defines one or more cylinders 16. A piston 18 and a cylinder head 20 may be associated with each cylinder 16 to form a combustion chamber 22. Specifically, piston 18 may be slidably disposed within each cylinder 16 to reciprocate between a top-dead-center (TDC) position and a bottom-dead-center (BDC) position, and cylinder head 20 may be positioned to cap off an end of cylinder 16, thereby forming combustion chamber 22. Engine 10 may include any number of combustion chambers 22 and combustion chambers 22 may be disposed in an “in-line” configuration, in a “V” configuration, in an opposing-piston configuration, or in any other suitable configuration.

Engine 10 may also include a crankshaft 24 rotatably disposed within engine block 14. A connecting rod 26 may connect each piston 18 to crankshaft 24 so that a sliding motion of piston 18 between the TDC and BDC positions within each respective cylinder 16 results in a rotation of crankshaft 24. Similarly, a rotation of crankshaft 24 may result in a sliding motion of piston 18 between the TDC and BDC positions. In a four-stroke engine, piston 18 may reciprocate between the TDC and BDC positions through an intake stroke, a compression stroke, a power stroke, and an exhaust stroke. In a two-stroke engine, piston 18 may reciprocate between the TDC and BDC positions through a power/exhaust/intake stroke and an intake/compression stroke.

Cylinder head 20 may define one or more fluid passages 28 associated with each combustion chamber 22 that are configured to direct gas (e.g., air and/or exhaust) or a mixture of gas and fluid (e.g., fuel) into or out of the associated chamber 22. In the disclosed embodiment, cylinder head 20 is shown as defining a single passage 28. Passage 28 may represent either an intake passage or an exhaust passage in this embodiment. It should be noted that, while only a single fluid passage 28 is shown, as many intake and/or exhaust passages may be provided within cylinder head 20 as desired. As an intake passage, passage 28 would be configured to deliver compressed air and/or an air and fuel mixture into a top end of combustion chamber 22. As an exhaust passage, passage 28 would be configured to direct exhaust and residual gases from the top end of combustion chamber 22 to the atmosphere. It is contemplated that, in some embodiments, only an exhaust passage may be formed within cylinder head 20 and the corresponding intake passage may instead be formed within engine block 14. In these configurations, the intake passage would be configured to direct air or the mixture of air and fuel radially inward to combustion chamber 22 through a side wall of cylinder 16.

A plurality of gas exchange valves 30 may be disposed within openings of passageway 28 and movable to selectively engage corresponding seats 32. Specifically, each valve 30 may be movable between a first position at which valve 30 is engaged with seat 32 to inhibit a flow of fluid through the opening, and a second position at which valve 30 is moved away from seat 32 (i.e., lifted) to allow a flow of fluid through the opening. The timing at which valve 30 is moved away from seat 32 (relative to a position of piston 18 between the TDC and BDC positions), as well as a lift height of valve 30 at the particular timing, may have an effect on the operation of engine 10. For example, the timing and lift height may affect production of emissions, production of power, fuel consumption, efficiency, temperature, pressure, etc. A spring 36 may be associated with each valve 30 and configured to bias valve 30 toward the first position and against seat 32. A spring retainer, not shown, may connect spring 36 to a stem end of each valve 30.

Valve actuation system 12 may be operatively engaged with cylinder head 20 and configured to simultaneously move valves 30 against the biases of springs 36 from their first positions toward their second positions at desired timings. It should be noted that, when each cylinder head 20 is provided within both intake and exhaust passages and corresponding intake and exhaust valves, engine 10 may include a separate valve actuation assembly for each set of intake and exhaust valves. Each valve actuation system 12 may include, among other things, a common camshaft 38, one or more pushrods 40, and a dedicated rocker arm 42.

Camshaft 38 may operatively engage crankshaft 24 in any manner readily apparent to one skilled in the art, where a rotation of crankshaft 24 results in a corresponding rotation of camshaft 38. For example, camshaft 38 may connect to crankshaft 24 through a gear train (not shown) that decreases the rotational speed of camshaft 38 to approximately one half of the rotational speed of crankshaft 24 (in the exemplary 4-stroke arrangement). Alternatively, camshaft 38 may connect to crankshaft 24 through a chain, a belt, or in any other appropriate manner. At least one cam lobe 44 may be connected to camshaft 38 and associated with each pairing of valves 30. An outer profile of cam lobe 44 may determine, at least in part, the actuation timing and lift profile of valves 30 during operation of engine 10.

Each pushrod 40 may reside in a cam follower that rides on and moves in accordance with the profile of cam lobe 44 as camshaft 38 rotates, and transfers a corresponding reciprocating motion to a first pivoting end of rocker arm 42. This reciprocating motion imparted to rocker arm 42 may cause rocker arm 42 to pivot about a shaft 46, thereby creating a corresponding reciprocating motion at an opposing second end of rocker arm 42 that lifts and releases valves 30. Thus, the rotation of camshaft 38 may cause valves 30 to move from the first position to the second position to create a specific lift pattern corresponding to the profile of cam lobe 44.

Rocker arm 42 may be connected to valves 30 by way of a valve bridge 48. Specifically, rocker arm 42 may include a pin 50 that is received within a second end of rocker arm 42, and a button 52 configured to receive an exposed end of pin 50. Button 52 may be able to swivel somewhat relative to pin 50, and includes a generally flat bottom surface that is configured to slide along a corresponding upper surface of valve bridge 48. The ability of button 52 to swivel and slide along the upper surface of valve bridge 48 may allow rocker arm 42 to transmit primarily vertical (i.e., axial) forces into valve bridge 48. The only horizontal (i.e., transverse) forces transmitted between rocker arm 42 and valve bridge 48 may be relatively low and due only to friction at the sliding interface between button 52 and bridge 48. This interface may be lubricated and/or polished to reduce the associated friction.

As can be seen in FIG. 2, valve actuation system 12 may include, among other things, one or more lash adjusters 54 disposed with an upper end of pushrod 40, and an adjusting screw 56 located within the first end of rocker arm 42. As will be described in more detail below, lash adjuster 54 may be configured to automatically adjust a clearance between a corresponding valve 30 and its associated seat 32 (and/or between other valve train components) when cam lobe 44 is rotated away from pushrod 40, while adjusting screw 56 may be configured to connect rocker arm 42 with pushrod 40 in a manually adjustable manner.

Lash adjuster 54 may embody any conventional type of adjuster that is configured to fill with oil as camshaft 38 rotates away from rocker arm 42, and then to internally trap the oil and function as a hydraulic link between pushrod 40 and rocker arm 42 as camshaft 38 rotates back toward rocker arm 42. In the disclosed embodiment, lash adjuster 54 is a check-valve type of adjuster having a valve element 58 that is spring biased against a seat 60. Valve element 58 may be pushed away from seat 60 during the retracting cam movement to fill an associated hydraulic chamber 62 with oil, and re-engage seat 60 during the extending cam movement to lock the oil inside hydraulic chamber 62. It is contemplated that lash adjuster 54 may have another form, if desired.

The oil directed to lash adjuster 54 may be provided via rocker shaft 46, rocker arm 42, and adjusting screw 56. Specifically, the oil may be pressurized by an engine-driven pump (not shown) and directed into a centralized axial passage 64 of shaft 46. The oil may then be directed outward via one or more radial passages 66 to an annular groove 68 that surrounds shaft 46. From annular groove 68, the oil may be directed to the opposing ends of rocker arm 42 via corresponding passages 70 and 72. The oil in passage 70 may lubricate pin 50, button 52, and valve bridge 48, while the oil in passage 72 may be directed through adjusting screw 56 to lash adjuster 54.

Adjusting screw 56 may disposed within a bore 74 of rocker arm 42 at the first end. In particular, as shown in FIGS. 3-4, adjusting screw 56 may include an elongated cylindrical shaft 76 having a first end 78, a second end 80, and an outer annular surface 82 that extends between first and second ends 78, 80. Threads 84 may be formed in outer annular surface 82 and configured to engage corresponding threads in bore 74 of rocker arm 42 (referring to FIG. 2). A tool engagement head 86 may be formed at first end 78 of shaft 76 and used to manually turn adjusting screw 56 and thereby selectively adjust an axial position of shaft 76 relative to rocker arm 42 (i.e., as adjusting screw 56 translates into and out of bore 74). In the disclosed embodiment, tool engagement head 86 may have an outer diameter that is the same as or less than an outer diameter of shaft 76. A lock nut 88 (shown only in FIGS. 1 and 2) may be provided to engage threads 84 adjacent tool engagement head 86 and to abut an upper surface of rocker arm 42, thereby inhibiting undesired axial movement of adjusting screw 56.

A pivot head 90 may be located at an end of shaft 76 opposite tool engagement head 86 and configured to engage lash adjuster 54 (e.g., to engage a spherical socket 91 formed in an upper end of lash adjuster 54—see FIG. 2). Pivot head 90 may have a rounded outer surface 92, and a planar shoulder 94 located opposite outer surface 92. Planar shoulder 94 may be generally orthogonal to an axis 96 of shaft 76. In the disclosed example, outer surface 92, together with shoulder 94, forms a hemispherical shape (e.g., surface 92 may arc through about 180°). An outer diameter of pivot head 90 may be larger than the outer diameter of shaft 76, for example about 40-50% larger. Outer surface 92 may be truncated at its vertex or center, such that pivot head 90 has a flat end face 98 that is generally orthogonal to axis 96. In one embodiment, end face 98 may have an outer diameter d that is about 45-55% of an outer diameter D of outer surface 92. When pivot head 90 is received within socket 91 of lash adjuster 54, the flattened nature of end face 98 may, together with socket 91, create a hemispherical void that functions to collect debris, which can subsequently be washed out of valve actuation system 12.

As described above, adjusting screw 56 may function to transport pressurized oil from rocker arm 42 (e.g., from passage 72) to lash adjuster 54. In particular, an axial passage 100 may be formed within shaft 76. Axial passage 100 may be a blind passage, extending from outer surface 92 to a location inside shaft 76 generally aligned with an outlet of passage 72 in rocker arm 42. A radial passage 102 may communicate passage 72 with axial passage 100. In some embodiments, an annular collection recess 104 (see FIG. 2) may be formed in bore 74 of rocker arm 42 at an opening of radial passage 102, such that oil from passage 72 may collect in this region before entering radial passage 102. This may facilitate oil flow into radial passage 102, regardless of the orientation of adjusting screw 56. A restrictive orifice 106 (shown only in FIG. 4) may be located inside radial passage 102 in order to provide a desired flow rate and/or pressure of fluid throughout (e.g., up stream of) valve actuation system 12.

One or more radial grooves 108 may be formed in pivot head 90 (e.g., within outer surface 92 and/or flat end face 98) that fluidly connect with axial passage 100. In the disclosed embodiment, radial groove 108 passes completely through an outlet of axial passage 100 (i.e., such that there are either two ends of one continuous groove or two separate grooves that meet at axial passage 100), and terminates short of shoulder 94. By terminating short of shoulder 94, a peripheral edge strength of pivot head 90 may be improved and sharp features (e.g., groove corners) that could cause damage to socket 91 of lash adjuster 54 may be avoided. It should be noted that, although radial groove 108 may terminate short of shoulder 94 at its outer ends, radial groove 108 may extend far enough to provide a relatively unrestricted flow of oil from passage 100 over a lip 109 of socket 91. That is, as adjusting screw 56 pivots within socket 91 of lash adjuster 54, the terminuses of radial groove 108 should extend out of socket 91 and clear lip 109 of socket 91 at least once per engine cycle, thereby ensuring an unrestricted flow of oil out of radial groove 108. In the disclosed embodiment, radial groove 108 may arc through an angle of about 155-160°.

Radial groove 108 is oriented generally orthogonal relative to an axis 110 of radial passage 102, in the disclosed example, and may have a curved or square bottom. It should be noted that other orientations of radial groove 108 may be possible, and allowing a variable orientation may improve manufacturability of adjusting screw 56. A width and a depth of radial groove 108 within outer surface 92 may be generally consistent (e.g., within manufacturing tolerances) along its length, and radial grooves 108 may be fabricated via a cold forming process. The shape and orientation or radial groove 108, along with the method of fabrication, may help to simplify manufacturing efforts and cost associated with adjusting screw 56.

A radius r of radial groove 108 may be about 0.4-0.6 times a radius R of axial passage 100, such that the flow from axial passage 100 may be divided into three streams of oil (i.e., a main stream available to lash adjuster 54, and two equal and smaller streams of oil flowing in opposite directions away from axial passage 100). These flows of oil may supply lash adjuster 54 with the oil necessary to set the clearance of valves 30 and, just as importantly, also function to draw heat away from the interface between pin 50 and lash adjuster 54 (e.g., between head 90 and socket 91).

INDUSTRIAL APPLICABILITY

The disclosed valve actuation system may have applicability with internal combustion engines. In particular, the disclosed valve actuation system may be used to lift one or more gas exchange valves of an engine, while maintaining a desired valve clearance during operation of the engine. In addition, the disclosed valve actuation system may have a unique adjusting screw that provides for cooling flows of oil to an interface with a lash adjuster disposed inside an associated pushrod. The cooling flows may be generated via radial grooves formed in a pivot head of the disclosed adjusting screw.

Several advantages may be associated with the disclosed adjusting screw. In particular, because radial grooves 108 may extend completely to axial passage 100 (i.e., without significant restriction at outer surface 92), a relatively low-pressure flow of oil may be used to cool and lubricate the interface between pivot head 90 and lash adjuster 54. In addition, this low-pressure oil may have a velocity that allows it to absorb a desired amount of heat from the interface. Further, the geometry of adjusting screw 56 may be relatively simple, robust, and inexpensive to fabricate.

It will be apparent to those skilled in the art that various modifications and variations can be made to the valve actuation system of the present disclosure without departing from the scope of the disclosure. Other embodiments will be apparent to those skilled in the art from consideration of the specification and practice of the embodiments disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope of the disclosure being indicated by the following claims. 

What is claimed is:
 1. An adjusting screw for a valve actuation system, the adjusting screw comprising: an elongated cylindrical shaft having a first end, a second end, and a threaded outer annular surface extending between the first and second ends; a head connected to the elongated cylindrical shaft at the first end and having a rounded outer surface; an axial passage formed in the elongated cylindrical shaft and passing through the head; and at least one radial groove formed in the rounded outer surface of the head and connected with the axial passage.
 2. The adjusting screw of claim 1, wherein the axial passage is a blind passage.
 3. The adjusting screw of claim 2, further including a radial passage formed in the elongated cylindrical shaft and extending from the axial passage through the rounded outer surface.
 4. The adjusting screw of claim 3, further including a restrictive orifice formed in the radial passage.
 5. The adjusting screw of claim 3, wherein the at least one radial groove is oriented generally orthogonal to an axis of the radial passage.
 6. The adjusting screw of claim 1, wherein the at least one radial groove passes through the axial passage.
 7. The adjusting screw of claim 1, wherein: the head includes a planar shoulder located opposite the rounded outer surface and oriented generally orthogonal to the axial passage; and the at least one radial groove terminates short of the planar shoulder.
 8. The adjusting screw of claim 1, wherein the at least one radial groove has a consistent width and depth along its length.
 9. The adjusting screw of claim 1, further including a tool engagement head located at the second end.
 10. The adjusting screw of claim 9, wherein an outer diameter of the tool engagement head has an outer diameter that is the same as or less than an outer diameter of the elongated cylindrical shaft.
 11. The adjusting screw of claim 1, wherein a radius of the at least one radial groove is about 0.4-0.6 times a radius of the axial passage.
 12. The adjusting screw of claim 11, wherein the head includes a flat end face formed at a center of the rounded outer surface around the axial passage.
 13. The adjusting screw of claim 12, wherein the flat end face has an outer diameter of 45-55% of outer diameter of the rounded outer surface.
 14. An adjusting screw for a valve actuation system, the adjusting screw comprising: an elongated cylindrical shaft having a first end, a second end, and a threaded outer annular surface extending between the first and second ends; a head connected to the elongated cylindrical shaft at the first end and having a rounded outer surface; an axial passage formed in the elongated cylindrical shaft and passing through the head; a flat end face formed at a center of the rounded outer surface around the axial passage; and at least one radial groove formed in the rounded outer surface of the head.
 15. The adjusting screw of claim 14, wherein the at least one radial groove is also formed in the flat end face.
 16. The adjusting screw of claim 14, further including: a radial passage formed in the elongated cylindrical shaft and extending from the axial passage through the rounded outer surface; and a restrictive orifice formed in the radial passage.
 17. The adjusting screw of claim 14, wherein: the head includes a planar shoulder located opposite the rounded outer surface and oriented generally orthogonal to the axial passage; and the at least one radial groove terminates short of the planar shoulder.
 18. The adjusting screw of claim 14, wherein the at least one radial groove has a consistent width and depth along its length.
 19. The adjusting screw of claim 14, further including a tool engagement head located at the second end, wherein an outer diameter of the tool engagement head has an outer diameter that is the same as or less than an outer diameter of the elongated cylindrical shaft.
 20. A valve assembly, comprising: at least one gas exchange valve; a shaft; a rocker arm pivotally connected to the shaft and having a first end operatively engaged with the at least one gas exchange valve, a second end with a threaded bore, and a passage extending from the shaft to the threaded bore; a pushrod having a cam end and a rocker arm end; a lash adjuster disposed in the rocker arm end of the pushrod; and an adjusting screw disposed in the second end of the rocker arm and configured to engage and fluidly supply the lash adjuster in the pushrod, the adjusting screw including: an elongated cylindrical shaft having a first end, a second end, and a threaded outer annular surface extending between the first and second ends; a head connected to the elongated cylindrical shaft at the first end and having a rounded outer surface and a flat end face formed at a center of the rounded outer surface; an axial passage formed in the elongated cylindrical shaft and passing through the flat end face of the head; radial passage formed in the elongated cylindrical shaft and extending from the threaded bore of the rocker arm to the axial passage; and at least one radial groove formed in the rounded outer surface of the head and passing through the axial passage. 